1. Department of Research and Evaluation, Kaiser Permanente Southern California , Pasadena, California , USA
2. Global Vaccines and Antivirals, Pfizer Inc , Collegeville, Pennsylvania , USA
3. Center for Integrated Health Care Research (CIHR), Kaiser Permanente Hawaii , Honolulu, Hawaii , USA
4. Department of Pediatric Infectious Diseases, Southern California Permanente Medical Group , Harbor City, California , USA